1. Field of the Invention
This invention relates to an improved process for the sulfonation of unsaturated fats and oils and the use of the sulfonated products in leather manufacture.
2. Statement of the Related Art
Stuffing agents for the manufacture of leather and skins are produced, inter alia, by the introduction of sulfonate and/or sulfate groups into unsaturated oils and fats. This gives water-soluble or water-emulsifiable compounds which are used in the fat-liquoring bath, optionally together with other standard auxiliaries such as emulsifiers or non-sulfonated oils.
Products of this type may be obtained by the reaction of fats containing unsaturated fractions with sulfuric acid, fuming sulfuric acid (oleum), or SO.sub.3, although in those cases--particularly where SO.sub.3 is used--dark-colored products are formed which are then bleached, unless sulfonation is carried out in the presence of large quantities of an inert solvent. To obtain substantially pure products of low neutralizing-agent-produced-salt content, sulfonation may also be carried out with a mixture of SO.sub.3 and air or inert gas although, in that instance, subsequent bleaching is again necessary (see British patent No. 989,669 and corresponding published German patent application No. 12 46 717).
The above-described difficulties in the sulfonation of fats containing unsaturated fractions are partly attributable to the fact that there is a considerable increase in viscosity during the reaction due to the formation of sulfonic acids or sulfuric acid esters. This impedes the further reaction, resulting in long contact times between the fats and the sulfonating agent and in dark colorations and carbonization. In addition, the increase in viscosity greatly reduces throughput in the apparatus used. In particular, the sulfonation reaction with a mixture of SO.sub.3 and air in falling-film or cascade reactors is seriously impeded by the increase in viscosity because it greatly reduces the rate of flow in the thin liquid layers, possibly resulting in complete blockage of the reactor. If the reaction is carried out at low temperatures, further difficulties arise through inhomogeneities in the fats.